Thanks Macrura. I just tested and it looks like you can do this:
// in site-settings.php
// note the toolbar line and inlineMode line
[
'name' => 'ckeditor_test',
'label' => 'CK Editor Test',
'type' => 'InputfieldCKEditor',
'width' => '100',
'description' => 'Some Formatted Test',
'collapsed' => 0,
'value' => '',
'toolbar' => "Bold, Italic",
'inlineMode' => 1,
],
Doing that will only show the Bold and Italic buttons in the CKeditor toolbar. It will also use inline mode. I'm not sure about the other stuff yet. I found those settings in wire/modules/Inputfield/InputfieldCKEditor/InputfieldCKEditor.module
Hope that helps someone.